Sorry IrnBru
Don't come from your part of Scotland so can't advise on marks, but if you have a lot of rock marks in your area, you could follow the exploits of the Arbroath to Aberdeen mob, and use similar baits etc.
Winter baits for cod are typically lug based cocktails tipped with squid, crab, rag, razor etc.
Summer baits will be crab based - but experimenting doesn't hurt.
Welcome to the site though, you will find plenty of tips to get you started.